The present invention relates to a method of making a photopolymer sleeve blank, and more particularly, to an improved method of making a photopolymer sleeve for use in flexographic printing applications that may be imaged by an end user.
Flexographic printing plates formed from photopolymerizable compositions are well known for use in printing applications. Such photopolymerizable compositions typically comprise at least an elastomeric binder, a monomer, and a photoinitiator. Upon exposure of the photopolymer plate from the back to actinic radiation, polymerization of the photopolymerizable layer occurs. This step is typically referred to as an initial “back exposure” step in which the polymerized portion of the cross-section of the printing plate is formed, which is referred to as the “floor.” The floor provides a foundation for the creation of a relief image on the plate. After the desired image of the printing plate is formed above the floor, the unexposed areas of the plate are removed, typically by washing with a solvent, to form a printing relief. However, when using individually attached plates in which the plates are wrapped around a print cylinder or print sleeve, a seam or void interrupts the image, causing a disruption or distortion in the printed image which is transferred to the substrate.
In more recent years, “seamless” hollow cylindrical sleeves have been developed which include a photopolymer layer as a support for various types of printing. For example, in one existing printing process and product (commercially available from OEC Graphics, Inc. under the designation SEAMEX®), a photopolymerizable material in the form of a flat sheet is wrapped around a metal or plastic sleeve and heated to fuse the ends and bond the photopolymerizable material to the sleeve. The photopolymerizable material is subjected to a back exposure step prior to wrapping the sleeve in order to achieve the required floor to support the details in the relief image. However, it is often desirable to produce a seamless photopolymer surface including an underlying cushion layer such as a cushioning foam. While the above described process can include such a cushion layer, it is very time consuming and limits the production volume.
In order to achieve high volumes of seamless photopolymer sleeves, no “floor” can be present due to the creation of disturbances in the seam during fusing which occurs because the floor and the unexposed photopolymer above the floor fuse under different conditions. Such is not possible with the above-described process because of the need to back expose and polymerize a floor prior to mounting the plate on a sleeve.
It would be desirable to be able to produce high volumes of photopolymer sleeves which include an unexposed photopolymer layer over a cushion layer. It would also be desirable to produce a blank photopolymer sleeve which can be readily provided with images by an end user to improve print quality.
Accordingly, there is still a need in the art for an improved method of making a photopolymer print sleeve for use in flexographic printing operations.